Fibers are ubiquitous materials that appear in a range of applications from natural and polymeric textile fabrics used in clothes to fibers made of silica glass that carry optical signals and can be fabricated in a variety of lengths, from a few centimeters to hundreds of kilometers. Typically, fibers are made of a single material, e.g., silica glass. Recently, new classes of fibers have emerged which combine a multiplicity of different materials. The different materials are arranged in specific geometries to enable functions such as transmission or reflection of light, detection of light, and thermal detection.